If it is the same woman, then the fact she has named a different father, the ages don't match and that she is claiming to be a spinster on her second marriage would suggest it isn't a straightforward case of a widow remarrying and that it may well be a bigamous marriage. A divorce would be be very unlikely, but needs to be ruled out.
The signature comparison is only relevant if you are looking at copies of the original register entries - if the certificates came from GRO , you won't be.